The present invention relates to a bubble trap for removing gas bubbles and, in some embodiments, also solids from a flowing liquid.
Bubble traps are commonly used where there is a need to remove gas bubbles from a flowing liquid, for example, in hydraulic circuits or in liquid chromatography. The presence of gas bubbles in the flowing liquid would be detrimental to the action of the functional parts of a hydraulic system or the integrity of the solid phase of a chromatography column.
Filters are commonly used where there is a need to remove solids from a flowing liquid, for example, in liquid chromatography. The solid may be, for example, an undissolved component of the chromatography column buffer or a solid present within the liquid sample. This is especially likely if the liquid sample is a biological sample.
In U.S. Pat. No. 4,806,135 a bubble trap is described for removal of emboli from blood prior to transfusion. The device allows blood to pass through a filter arranged so that solid components, such as red blood cells, pass through the filter but entrained bubbles do not. This separation is achieved by introducing the blood in a tangential direction relative to the axis of rotation of the chamber. The introduction of the blood is above the level of the filter and with a low velocity so the bubbles rise from the blood as the blood rotates within the body of the bubble trap before reaching a filter below the level of the fluid inlet. The filter can be a wide mesh filter as it is not required to trap bubbles.
Frequently there is a need to remove gas bubbles efficiently from a rapidly flowing liquid which U.S. Pat. No. 4,806,135 cannot perform. In other cases the removal of both gas bubbles and solids from a rapidly flowing liquid is required. Typically the removal of both gas bubbles and solid components from a rapidly flowing liquid has necessitated the use of a filter and a bubble trap arranged in series, each independently performing its function.
There is therefore a need for simple compact devices that can perform the removal of bubbles, or both bubbles and solids, from a rapidly flowing liquid.
The flow of the liquid is directed from the inlet to impinge upon the barrier which causes bubbles present within the flow of the liquid to coalesce on the surface of the barrier and then float to the top of the bubble trap.
When the bubble trap of the invention combines the functions of a filter with a bubble trap the barrier takes the form of a filter covering the outlet. The bubble trap may have a plurality of filters and outlets. The filter has openings of a diameter which prevent the passage of bubbles through the filter. The surface tension of the liquid covering the filter openings is quite strong and it requires a considerable trans-filter pressure differential to force the bubbles through the filter openings. The bubbles may then aggregate before they float free from the surface of the filter or be dislodged by the flow of the liquid onto the filter surface.
The upper and lower levels of the liquid within the chamber may be regulated by a sensor to be maintained above the top of the filter.
The bubble trap is arranged to avoid vortex formation in the liquid as vortex formation could lower the liquid level sufficiently to allow air through the filter.
Conveniently the chamber is generally cylindrical in which case vortex formation in the chamber can be avoided by positioning the filter, and optionally filter outlet, off the central axis of the chamber.
Preferably the inlet has one or more vertically aligned orifices directed to produce circumferential flow of the liquid. Impingement of the liquid upon the filter also acts to dislodge coalesced bubbles on the filter surface.
An inlet with a plurality of orifices provides circumferential flow of the liquid throughout the entire height of the filter such that the liquid impinges more effectively upon the filter and ensures good vertical distribution of liquid over a wide range of flow rates.
Conveniently, the one or more orifices are selected from slits, holes and nozzles or any of the types of orifice known to those skilled in the art.
Preferably the filter openings are less than 1.2 im. A typical flow rate for the bubble trap would be 5-40 liters/min. A low liquid residence time is desirable, such a residence time is typically 30-3 seconds. The effective size of the opening is dependent upon several factors, for example, the viscosity of the liquid and the internal pressure of the bubble chamber.
Preferably if sterile filtration is required the opening size should be less than 0.22 im.
Preferably the filter may be a removable cartridge filter. The size of the cartridge filter, and of the inlet, reduce the interior volume of the chamber so reducing the stagnant holding volume of the chamber. Such cartridge filters are widely available having a wide range of opening sizes and structural tolerances. Such filter cartridges are available in a number of standard lengths which can be used interchangeably within the limitation of the maximum size of the bubble trap chamber. For example, MILLIGARD(trademark) Standard and MILLIGARD(trademark) Low Protein-Binding Cartridge filters may be used, both manufactured by Millipore Corporation, US. Preferably these filters may be either 4xe2x80x3 or 10xe2x80x3 in height.
The presence of the filter in the bubble trap device results in a small interior volume to minimise the stagnant or holding volume. It is capable of sterile operation, if such is required, and has a minimum number of easy-to-produce components. The simple construction reduces the need for complex valving arrangements and associated hardware. The general design of the device is sanitary to enable cleaning of the device with, for example, sanitizing chemicals or steam. The replacement of the cartridge is possible whilst remaining sterile.